Direct measurement of lanthanum uptake and distribution in internodal cells of Chara

Rare earth elements (REEs) influence many physiological processes in plants, but the mechanism is still unknown. The question of whether REEs can enter plant cells is crucial in assessing the biological effects of REEs. In this paper, a method for determination of REE lanthanum (La) in ultratrace level in cell contents of giant algal cells was established. The uptake and subcellular distribution of La in internodal cells of Chara corallina were investigated. After incubation with 6 μM LaCl₃ for 72 h, about 0.523% of total lanthanum in the whole cell was internalized. Approximately 55% of the total intracellular lanthanum was in the cytoplasm, and lanthanum concentration in the cytoplasm was much higher than that in the vacuole. The concentration dependence of La³⁺ uptake occurred in a biphasic manner, which was tentatively attributed to the operation of two separate transport systems, a high-affinity system which is saturated at 10 μM and a low affinity system which showed a linear dependence on concentration up to at least 100 μM. Only the high-affinity system was studied in detail. Effects of channel activator, blocker and metabolic inhibition on lanthanum uptake through this system were investigated. The results suggest that lanthanum transport across plasma membrane was a metabolically mediated process and membrane potential difference was independent of lanthanum uptake.